1. Field of the Invention
The present invention relates to a spot welding inspecting apparatus which is mounted in a spot welding gun and capable of inspecting a welded portion by an ultrasonic sensor.
2. Background Art
In spot welding, a weld metal molten and solidified at a contact portion of, for example, two sheets of steel plates after welding is referred to as a nugget. A bonding strength of a welded portion is evaluated by a nugget diameter indicating a size of the nugget.
In inspecting after welding, as an apparatus of measuring the nugget diameter utilizing a nondestructive inspection method, there is proposed an electrode including an ultrasonic probe at inside thereof (refer to, for example, Patent Reference 1).
[Patent Reference 1] JP-T-2005-527374 (FIG. 1, FIG. 2)
Patent Reference 1 will be explained in reference to the following drawings.
FIG. 15 is a view for explaining a basic constitution of a related art. A welding electrode 100 is constituted by a shaft 102, an ultrasonic probe 106, a probe holder 107, a cooling water pipe 108, and a signal line 109. The shaft 102 has a hollow shape and is attached with a welding cap 101 at a front end thereof. The ultrasonic probe 106 is mounted in the welding cap 101 and a front end portion 105 of the shaft 102 by way of a connection pad 104 placed at an inner bottom portion 103 of the welding cap 101. The probe holder 107 holds the ultrasonic probe 106 from a rear side and is inserted into the shaft 102.
The cooling water pipe 108 extends from the probe holder 107 and is inserted into the shaft 102. The signal line 109 extends from a rear end of the ultrasonic probe 106 to an upper side of the drawing and is inserted into the probe holder 107 and the cooling water pipe 108.
According to the welding electrode 100 of Patent Reference 1, as shown by arrow marks, cooling water flows from a rear end portion 111 of the cooling water pipe 108. The cooling water passes a periphery of the ultrasonic probe 106 by way of an inner portion of the probe holder 107. The cooling water changes a flowing direction at the inner bottom portion of the welding cap 101. Then, the cooling water flows along the periphery of the ultrasonic probe 106 and a partition plate 112 attached to a lower portion of the probe holder 107. Finally, the cooling water flows out from a rear end portion 113 of the shaft 102 in the hollow shape as indicated by arrow marks.
The welding electrode 100 can be cooled by the flow of the cooling water.
The inventors have carried out spot welding by using a welding electrode having a structure of the welding electrode 100 of Patent Reference 1, and tried to inspect a bonding portion immediately thereafter. As a result thereof, the cooling water flowing at an inner portion of the welding electrode 100 flows deviatedly in a constant direction to be along the partition plate 112. Therefore, it has been found that cooling of the welding cap 101 is deviated.
The cooling water at the inner portion of the welding electrode 100 is divided in two to a side (cool water side) in which cooling is positively carried out by passing the cooling water and a side (warm water side) in which the cooling water is not supplied sufficiently and cooling becomes insufficient by receiving heat from the welded portion. Therefore, the ultrasonic probe 106 is dipped to both sides of the cool water side and the warm water side. So, there is a concern of bringing about a deterioration in a measurement accuracy and a reduction in a durability by thermal shock in the ultrasonic probe 106 by heat transmitted from the warm water side.
In addition thereto, in FIG. 2 of Patent Reference 1, according to the welding electrode, a pad 16 and a welding cap 12 are brought into close contact with each other by pressing a probe 14 by a spring element. However, there is a case in which the pad 16 and the welding cap 12 are insufficiently brought into close contact with each other to hamper transmission of an ultrasonic signal.